The present invention relates to a process for fabricating interconnection of a semiconductor device based on physical vapor deposition (PVD) and a so-called high temperature reflow process.
With increasing demand for more highly integrated semiconductor devices, finer size rules are required. In the process for fabricating interconnections of semiconductor devices, the technology for forming narrower and deeper (i.e., higher aspect ratio) contact holes, via holes, and through holes (referred to collectively hereinafter as "connection holes") is highly estimated as the key of the device fabrication process. A connection hole can be formed by, for instance, providing an aperture portion in the insulating layer formed on the upper side of a conductive layer, and then filling the aperture portion with a metallic interconnection material. In case of depositing a film of a metallic interconnection material by sputtering an aluminum (Al) based alloy on an insulating film with an aperture portion formed therein, no sputtered aluminum-based alloy particles are found incident on the portion shielded by the side wall of the aperture portion. This phenomenon is known as a so-called shadowing effect. Thus, an aperture portion with inferior aluminum-based alloy coverage remains as a result. This induces a problematic device failure such as disconnection in the vicinity of the bottom portion of the aperture where less aluminum based alloy is deposited. It is therefore required to establish a process technology to surely fill the aperture portion with a metallic interconnection material.
High temperature aluminum reflow process is proposed as the process technology to meet the demand above. The process comprises depositing an aluminum based alloy on the insulating film by means of sputtering, and then applying heat treatment thereto to fill the aperture portion with the flow of the aluminum based alloy. To fill the aperture portion with the aluminum based alloy by applying high temperature aluminum reflow treatment, the aluminum based alloy is heated in a temperature range not lower than the recrystallization temperature (although depending on the composition of the alloy, it is generally 350.degree. C. or higher) but not higher than the melting point thereof. In this manner, the aluminum based alloy film deposited on the insulating layer is fluidized and then settles inside the aperture portion to give an aperture portion filled with the aluminum based alloy. To prevent the surface of the aluminum based alloy from being oxidized and to favorably introduce the flow of the alloy into the aperture portion, preferably, the film deposition of the aluminum based alloy and the reflow treatment thereof are performed inside a same film deposition apparatus without exposing the aluminum based alloy to air.
In some cases of high temperature aluminum reflow treatment, furthermore, high pressure is applied under an inert gas atmosphere during reflow treatment in order to achieve an aperture portion more favorably filled with an aluminum based alloy and to lower the reflow temperature. This type of reflow treatment is referred to hereinafter as a "high pressure reflow treatment". Also in this process, the flow of the alloy can be more favorably introduced into the aperture portion by performing the film deposition of the aluminum based alloy and the reflow treatment thereof inside a same film deposition apparatus without exposing the aluminum based alloy to air.
A schematically drawn partial cross sectional view of a semiconductor substrate and the like subjected to film deposition of an aluminum based alloy and to reflow treatment in the same film deposition apparatus without exposing the aluminum based alloy to air is shown in FIGS. 1(A) and 1(B). FIG. 2 shows a schematically drawn partial sectional view of another semiconductor substrate and the like that is exposed to air after depositing the aluminum based alloy and then subjected to reflow treatment. In the figures, it can be seen that the semiconductor substrate indicated by reference numeral 130 comprises thereon an element isolating region 131, a gate electrode 133, a source/drain region 135, an insulating layer 140 formed on the surface of the semiconductor substrate 130, an aperture portion 136 formed on the insulating layer 140, a so-called adhesive layer 141, and an aluminum based alloy layer 142. FIG. 1(A) is a schematically drawn partial cross sectional view of the structure obtained after depositing the aluminum based alloy layer 142 on the surface of the insulating layer 140. FIG. 1(B) shows a schematically drawn partial cross sectional view of the structure obtained after reflow treatment.
Referring to FIG. 2, voids tend to generate in the bottom portion of the aperture portion 136 when reflow treatment is effected after depositing the aluminum based alloy which is further exposed to air, because the aluminum alloy subjected to reflow treatment flows into the aperture portion 136 only insufficiently. Thus, it is necessary to deposit the aluminum based alloy and to perform the reflow treatment in a same film deposition apparatus. To perform the treatment above in a single film deposition apparatus, however, a clustered equipment comprising both the film deposition chamber and the reflow (or the high pressure reflow) treatment chamber is necessary. Such a film deposition apparatus is too expensive, and the use of such an apparatus leads to the increase in cost of production.
In addition, when the reflow treatment is carried out in a separated apparatus after depositing the aluminum based alloy, a cleaning process becomes necessary immediately before the reflow treatment in order to remove an oxidized film formed on the surface of the aluminum based alloy layer 142 by means such as sputter-etching. However, carrying out the cleaning process and the reflow treatment in the same apparatus requires an expensive apparatus that leads to increased production cost.
Accordingly, an object of the present invention is to provide a process for fabricating an interconnection for a semiconductor device in which, for instance, deposition of a metallic interconnection material such as an aluminum based alloy by means of physical vapor deposition and the reflow treatment thereafter are performed without using the same film deposition apparatus, and the metallic interconnection material is subjected to reflow treatment without previous surface treatment.